New ferroelectric materials and process of preparation

ABSTRACT

New transparent ferroelectric compositions have been prepared having a tetragonal tungsten-bronze-type crystallographic structure and having the formula x(ANbO3) . (1-x) MNb2O6 where A is at least one alkali metal ion and M is an alkaline earth metal ion and where x can be from 0.12 to 0.50. These materials have large dielectric constants, ( Epsilon ), and linear electro-optic coefficients (r), at room temperature. The value of r is significantly larger than that of LiNbO3. These materials have great potential as light modulators and deflectors.

O United States Patent [151 3,640,865 Burns et al. 1 Feb. 8, 1972 [54]NEW FERROELECTRIC MATERIALS AND PROCESS OF PREPARATION References Cited[72] Inventors: Gerald Burns, Yorktown Heights; Edward UNITED STATESPATENTS A. Giess Somers; Daniel F. OKane, Katonahian of 3,423,686 1/1969Ballman et al. ..252/62.9 X

[73] Assignee: International Business Machines Corpora- PrimaryExaminerJames E. Poer tion, Armonk, NY. Assistant Examiner.l. Cooper[22] Filed: Apr. 9 1970 Att0meyHamfin and Jancm and Hansel L. McGee 21]Appl. No.: 27,111 [57 ABSTRACT Related Application Dam New transparentferroelectric Compositions have been prepared having a tetragonaltungsten-bronze-type crystallol commuatlomm'paft P 3 y 5, graphicstructure and having the formula x(ANb0 (l-x) I 1969, abandoned, which13 a contlnuanon-ln-pifn 9 MNb O where A is at least one alkali metalion and M is an al- 3 y 15, 1968, abandoned, whlch 1S kaline earth metalion and where x can be from 0.12 to 0.50. a commuatlon'm'pal't of 9 7These materials have large dielectric constants, (e),and linear 1968,abandoned. electro-optic coefficients (r), at room temperature. Thevalue of r is significantly larger than that of LiNbO These materials[52] US. Cl ..252/62.9, 23/302, 23/304 have great potential as lightmodulate and d fl t [51] Int. Cl. ..C04b 35/00, C04b 35/60 [58] Field ofSearch ..252/62.9; 23/301, 302, 304 27 Claims, 8 Drawing Figures PAIENmmam:

SHEET 1 BF FIG. 1

40 80 120 160 200 240 TEMPERATURE (C) FIG. 2

x 14 cm I OH x= 6328A O 10 nz2.25 I l D. l a

O 2 05 6 l- O (D 4 5 as o 2/ O: 1 1 1 L 1 l O TEMPERATURE C INVENTORSGERALD BURNS EDWARD A. GIESS DANIEL F. O'KANE ATTORNEY PAIENTEnrEn a maSHEET 2 OF 5 F l G. 3

1! U0 wmazmmazfi KNbO (SS) KNbO3 MOLE SrNbz e KNbO "SrNb O SYSTEM PHASEDIAGRAM PAIENYEB 19 2 311m 3 OF 5 BONb O 459 q\ PHASE DIAGAM LUBRONZEiSS) BRONZE(SS)+LIQ. A 2 e q u) n: m E 1200 I] E N E KBo Nb O m Il 1100 1083i4 j/KNbO (SS) m KNbO (SS)-1-BRONZE(SS) o 40 so 00 BGNbzOsmanure: 'amz 3.640.865

SHEET 5 BF 5 BaNbzoe XAMMW NEW FERROELECTRIC MATERIALS AND PROCESS OFPREPARATION This application is a continuation-in-part of copending andnow abandoned patent application Ser. No. 821,779, filed on May 5, 1969which was a continuation-in-part of copending and now abandoned patentapplication Serial No. 753,823, filed on July 15, 1968. which was inturn a continuation-inpart of the copending and now abandoned patentapplication Serial No. 694,916, filed on Jan. 2, 1968.

DESCRIPTION OF THE PRIOR ART It has been the object of considerableresearch to provide ferroelectric materials of high purity exhibitinguseful physical properties. Such materials find ready application innumerous devices well known in the art. Niobate ceramic compositionshave been of particular interest to the researcher. These compositions,because of their high dielectric constants and Curie temperatures, belowwhich they are ferroelectric, have been highly considered inpiezoelectric devices, capacitors and modulators.

Compositions of this kind which have been described include alkali metalion metaniobates, for example, those having the chemical formulas NaNbOKNbO and LiNbO alkaline earth metal ion niobates, e.g., those having thechemical formulas BaNb O Ba Nb O and the corresponding compounds ofcalcium and strontium; and niobates of zinc, cadmium and lead, e.g.,those having the chemical formulas Zn Nb O-,, Cd Nb O, Pb Nb O and PbNbO Additionally, mixed metal niobates have also been prepared. In US.Pat. No. 2,864,713 to Brian Lewis, there is shown and described acomposition having the general formula (I-X)L2O'XMR2O6 where L is Na orK, M is Cd or Pb, and R is Nb. These materials are found to have theperovskite crystallographic structure.

Another example of mixed niobates is disclosed in US. Pat. No. 2,805,175to Gilbert Goodman showing principally lead niobate compositions havingthe general formula (Pb, A )'(NbO where A represents an element selectedfrom the group consisting of Mg, Ca, Ba and Sr and mixtures thereof.However, these materials do not contain any alkali metal oxide. Further,they have in general been found to have the orthorhombic tungsten-bronzecrystallographic structure.

While the compositions in the above-cited patents have found use astemperature sensing elements in control apparatii, transducers andcapacitor applications, they have in general found little use inelectro-optic applications, such as light modulators and deflectors,This is to be expected, since most of these materials are ceramic andare in general not transparent to light.

SUMMARY OF THE INVENTION A group of ferroelectric materials has beenprepared, the members of which have the tetragonal tungsten-bronze typestructure as opposed to the perovskite-type structure of like materialsdescribed in the prior art. By tetragonal is meant that the latticeconstants of the crystals (a, and b,,) are equal for a standarddeviation of 0.2 percent. These materials have the general formulax(ANbO lx)MNb O where A is at least one metal selected from the groupconsisting of Li, Na, K, and Rb and M is a metal selected from the groupconsisting of Ca, Sr and Ba; and where x can be from about 0.12 to 0.50.The preferred range of x is from about 0.12 to about 0.35. Additionallymixed alkali metal analogs are prepared and have the general formula A A,M Nb O, where A is a first alkali metal ion, A is a second alkali metalion, M is an alkaline earth metal ion and 0 x l.0. These materials aregrown as optically transparent single crystals, thus are suitable forelectro-optic applications.

It is an object of the invention to provide a new class of ferroelectricmaterials which can be used in electro-optic applications.

A further object of the invention is to provide a new class offerroelectric materials having the tetragonal tunsten-bronze typecrystallographic structure.

Another object of the invention is to provide a new class offerroelectric materials which are transparent to light and which has thegeneral formula x( ANbO lx)MNb,O where A is a metal selected from atleast one of the alkali metal, M is a metal selected from an alkalineearth metal, and x can havea value offrom 0.12 to 0.50.

And still another object of the invention is to provide a new class offenroelectn'c materials which are transparent to light and which has theformula A,A ,M Nb O, where A is a first alkali metal ion, A is a secondalkali metal ion different from A, M is an alkaline earth metal ion andO x l .0.

And yet another object of the invention is to provide a method forpreparing crystalline single-phased solid solutions of a new class offerroelectric compositions having the general formula x( ANbO l-x)MnbO.;, where A is a metal selected from at least one of the alkali metals,M is a metal selected from the alkaline earth metals and x can have avalue of from 0.12 to 0.35.

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of preferred embodiments of the invention, as illustrated inthe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows the 10 c.p.s. dielectricconstant parallel and perpendicular to the tetragonal c-axis for KSr NbO,

FIG. 2 shows the DC parallel electro-optic constant (r) plotted againsttemperature for KSr Nb O,

FIG. 3 shows the phase diagram for the KNbO SrNb O system.

FIG. 4 shows the phase diagram for the KNbO -BaNb O system.

FIG. 5 is the phase diagram for the NaNbO BaNb O system.

FIG. 6 is a ternary diagram indicating the area of ternary meltcompositions from which single crystals of the NaNbO;, BaNb O system canbe grown.

FIG. 7 is a ternary diagram illustrating the region of ternary meltcomposition from which single crystals of the ternarysystem-KnbO;,-NaNbO BaNb O system are grown. The melt compositions()needed to obtain various pulled crystal compositions are shown.

FIG. 8 is a ternary diagram illustrating the region of ternary meltcomposition from which single crystals of the ternary system, RbNbO-NaNbO BaNb O are grown. The melt compositions needed to obtain variouspulled crystal compositions are shown.

DESCRIPTION OF PREFERRED EMBODIMENTS This invention is based upon adiscovery that single-phased solid solutions of transparentferroelectric materials can be prepared directly from a melt containingthe individual constituents. The materials are prepared from appropriateamounts of alkali metal and alkaline earth metal carbonates and niobiumoxide. The reaction of the constituents may be characterized by thefollowing equations:

2M00 (1--x)MCO3 (1-2) Nb O (ANbO -(MNb;0 1-3002; gloom 511400:

+ gNbzofi mNbos) mnmo 200, where gumbo -(MNbz0a)=AM2Nb5015- Theferroelectric compositions are prepared from high-purity startingmaterials. The carbonates, A CO where A is an alkali metal selected fromLi, Na, K, and Rb, and MCO where M is an alkaline earth metal selectedfrom Ca, Sr and Ba, contain less than 10 ppm. impurities and the niobiumoxide (Nb O used contains less than 0.03 percent Ta and 10 p.p.m. ofother impurities. Stoichiometric quantities of the carbonates and oxideare added to a platinum crucible and heated in an oxygen atmosphere to atemperature between about l,l to about l,500 C. to provide a melt. Themelt is found to have binary compositions according to the followinggeneral formula:

xANbO b.( lx)MNb O whereA is at least one alkali metal ion, M is analkaline earth metal ion and x can be from 0.12 to 0.98. Preferred meltcompositions from which crystalline single-phase solid solutions can begrown, are exemplified by the following systems:

xNaNbO l-x)BaNb O where x=0.77 to 0.15 (mole fractions);

xKNbO b.( lx)BaNb O where x=0.98 to 0.38 (mole fractions), and

xKNbO b.(lx)SrNb O where x=0.98 to 0.12 (mole fractions).

Single crystals which are single-phase solid solutions can be pulledfrom the above melts with a seed crystal or by seeding on to a Pt-Rhrod. After a sufficient length of crystal is grown, the melt is cooledslowly to room temperature at a rate of about 5 to 15 C. per hour.During the cooling, single crystals of the solid solution compositioncrystallize from the melt in the crucible.

Alternately,.the compositions may be prepared by heating appropriateamounts of the alkali metal niobate (ANbO and the alkaline earth metalniobate (MNb O in a platinum crucible. The mixture is heated at atemperature between l,l00 to 1,500 C. to provide a melt having the abovecomposition from which single crystals are grown. The resulting reactionis described in the equation below:

ANbO -l-MNb O -*AM l lb O Single crystalline tungsten-bronze type solidsolutions grown as products of the above alternate methods and from theabove exemplified melt compositions can be characterized as follows:

xNaNbO l-x)BaNb O where x=0.35 to 0.15 mole fractions;

xRbNbO lx)BaNb O where F030 to 0.35 mole frac- 4O xlzifffss bikxlBaNb Owhere x=0.35 to 0.25 mole fracxiiib, 1-. s.-b.0, where 1:030 to 0.40mole fracxK l: b b.(lx)SrNb O,-,, where x=0.45 to 0.12 mole fractions.

a b c d Na,co, 20 10 I3 20 B300, 30 4o 42 as N t o, so so 45 4s Thevalues given are in mole percent. The materials prepared by the abovegenerally described methods are found to be transparent ferroelectricmaterials.

They have Curie temperatures (T in the range of about 585 C. dielectricconstants, measured at room temperature, in the range of about 1,000 to50, and electro-optic constants (r), i.e., (the response of the crystalto a field E along the caxis, with light traveling along the a-axis inthe range of l.3 l0"B&8 cm./volt or a half-wave voltage of about 500volts. This half-wave voltage can be considerably reduced by operatingat temperatures somewhat above room temperature as can be seen in FlG.2. This voltage can also be reduced by suitably 75 doping the crystalsso that the transition temperature is brought closer to roomtemperature. The constant (r) can be abut six or seven times greaterthan (r) found for LiNbO a material generally considered to be one ofthe best materials for use on electro-optic devices. Pycnometric densitymeasurements made on the materials indicate densities of about 5.0g./cc., which corresponds to two molecules of AM Nb O, per tetragonalunit cell.

Additionally ternary compositions have been prepared hav- 0 ing theformula A A',-,M Nb O, where A is a first alkali metal ion, A is asecond alkali metal ion and is different from A, and M is an alkalineearth metal ion and 0 x l .0, where A potassium and A sodium.

Illustrative of these ternary compositions are the KNbO NaNbO -BaNb Oand RbNbO NaNbO -BaNb O systems. These compositions can also be giventhe general formula (ANbO (A'NbO ),,(MNb O where A is a firstalkalimetal ion, A is a second alkali metal ion difi'erent from A, M isa metal selected from the alkaline earth metals of the periodic tableand x is about 1.5 to about 16.3, y is about L6 to about 26.5 and z isabout 72.0 to about 94.0. The values of x, y and z are ascertained fromthe value of the arrowheads shown in FIGS. 7 and 8. For the KNbO -NaNbOBaNb O system it is seen in the ternary phase diagram of FIG. 7, thatcrystals are pulled from a relative triangular region of diagram withend points near NaBa Nb O K Na Ba Nb O and (NaNbO O The crystals arepulled from melts represented by (0); the arrows show the composition ofthe pulled crystal from each melt. Crystals pulled from the indicatedmelt composition region are found to have the tetragonal or orthorhombictungsten-bronze type structure which usually have higher BaNb O andlower KNbO concentrations and only slight changes in the NaNbO content.Within the triangular region the shaded area contains compositions witha tetragonal tungsten bronze structure, and outside the shaded area thestructure is an orthorhombic tungsten-bronze. In a preferred embodimentof the invention, crystals are pulled from a melt having a compositionof K,- Na Ba Nb O where 0.5 x 0.9 to obtain the tetragonaltungsten-bronze structure. Crystals pulled from the melt compositionsnear (KNbO ),.,(NaNbO )BaNbO are also found to be tetragonal bronzecrystals.

For the RbNbO -NaNbO -BaNb O ternary system, see FIG. 8, orthorhombictungsten bronze crystals are produced along the arrows from meltcompositions represented by (0) in the triangular area beneath thedashed line and bounded by NaBa Nb 0l5, Rb =,Na Ba Nb O, and (NaNbO,,,(BaNb 0 The pulled crystals usually have higher BaNb O lower RbNbOand slight changes in the NaNbO concentrations. For example, a melt of(966.7] can be used to obtain a single crystal of (RbNb0 (NaNbO (BaNbThis crystal had a Curie temperature of 558 C. and the microtwinsdisappeared near 240 C. Cooling below 300 C. with pressure applied alongthe [I00] direction of the orthohombic cell results in the removal ofmicrotwins.

Crystals as pulled or grown from the melt compositions are found to havea higher Na-to-K. ratio than the melt composition ternary. These ternarymetal niobate compositions are found not to have twinned crystalstructures or have twinned structures which disappear at relatively lowtemperatures. These materials have similar electro-optical properties tothe above binary compositions.

In order that those skilled in the art may better understand how thepresent invention may be practiced, the following examples are given byway of illustration and not by way of limitation.

EXAMPLE I A thoroughly mixed charge of 400' grams comprising 26.9 gramsof powdered K CO 1 14.8 grams of powdered SrCO and 258.3 grams ofpowdered Nb O is loaded in a platinum crucible which is placed in aCzochralski-type crystal pulling apparatus. The crucible and itscontents are heated in an oxygen atmosphere at l,500 C. to form a meltof KSr Nb O, A solid solution single crystal was pulled from the melt atapproximately 10 mm./hr. After a sufficient length was grown, thecrystal was removed from the melt and held about 5 mm. above the meltsurface during the cooling of the crucible at 5 to 15 C./hr. Largesingle crystals (1 l 1 cm?) also grew on the surface of the frozen meltin the platinum crucible. The resulting pulled crystal weighed 20 gramsand had a specific gravity of 5.0. The phase diagram shown in FIG. 3shows no appreciable change in composition of the pulled crystal whenthe melt composition is KSr Nb O or [(KNb (SrNb O The crystal pulledfrom KSr Nb O, melt composition exhibited a dielectric anomaly at about156 C. and peak dielectric constant was 1.4X". The crystal melted atabout l,470 Cil0 C.

The homogeneity of the crystals thus prepared was demonstrated by thecharacter of the plots of dielectric constant versus temperature asshown in FIG. 1. FIG. 1 shows the 104 c.p.s.

dielectric constant parallel (e) and perpendicular (e) to the tetragonalc-axis for xsr.Nb o,.. As seen in the figure, e at room temperature isabout 10 and peaks above 10. The transition temperature is found to berelatively independent of composition within the solubility range. Abovethe transition temperature, a Curie law e=C/(TT is found to hold for thecrystals measured with C in the 2 to 4 l0 C. range. Hysteresis loopshave been measured on a modified Sawyer-Tower circuit at 30 c.p.s. P.(the spontaneous polarization) is p. C/cm. C. below the Curietemperature. At about 160 C.,

the electric field becomes linear for moderate values of E. The roomtemperature coercive field is about 20,000 v./cm., thus the crystals canbe poled easily, i.e., made into a single domain.

FIG. 2 shows the DC parallel electro-optic constant r n,,/n" r, plottedagainst temperature. This constant describes the response of the crystalto a field E along the caxis, with the light traveling along the a-axis.The indices n and n are the ordinary and extraordinary indices,respectively, and are approximately equal to 2.25. The field inducedbirefringence as measured at 6,328 A. with a quarter-wave plate andpolarizer. The relation between the measured retardation F and r wastaken to be ll n r lE/a where l is the optical path length in thecrystal and a is wavelength. The room temperature value of r is 1.3 10cm./volt, as compared to 0. l 8X10 cm./volt for LiNbO In a similarmanner many different solid solution compositions in the series wereprepared. The dielectric constant at the Curie temperature of thecompositions together with the lattice constants (a and c given inangstroms are indicated in the ensuing Table l. The foregoing materialswere prepared by mixing appropriate amounts of starting materials andheating them at appropriate temperatures. The melt compositions fromwhich the crystals can be grown is easily gleaned from the phasediagrams of FIGS. 3, 4 and 5.

TABLE I M.P Dielectric a0 co 5:1 'Ic constant at Examples Composition(A.) (A.) C.) 0.) room temp.

2 NaBarNbrom 12.47 3.982 1,420 585 190 KSIzNbsOls... 12.47 3.942 1,470156 230 KBBaNbsOw" 12.55 4.010 1,405 373 360 RbSr2NbrOrs. 12.51 3.949 1,407 139 256 6 RbB8QNb5015 12.58 4.024 1,395

EXAMPLE 7 In preparing crystals from ternary melt compositions accordingto the ternary diagram of FIG. 7, a thoroughly mixed charge of 420 gramscomprising 20.64 grams of powdered K CO 3.96 grams of powdered Na CO147.34 grams of powdered BaCO and 248.06 grams of powdered Nb O isloaded in a platinum crucible which is placed in a Czochralskitypecrystal pulling apparatus. The crucible and its contents are heated inan oxygen atmosphere at 1,480 C. to form a ternary melt material havingthe formula o.a a Ba Nb O (KNbO (BaNb O A single crystal was pulled fromthe melt at the rate of 7 mm./hr., with a rotation rate of approximatelyrpm. and in an oxygen atmosphere. The crystal is removed from the meltand held about 5 mm. above the melt surfaces during the cooling of thecrucible at a rate of about 5 C./hr., for the first 300 C. and then at15 C./hr., to room temperature. The crystal had compositioncorresponding to the following formula:

The resulting pulled crystal had a diameter of about 8 mm. and was 40mm. long. The crystal weighed 10 grams and had a specific gravity of5.0. The crystal exhibited a dielectric anomaly at 420 C. and the peakdielectric constant was 190,000. The crystal melted at about 1,4l0 C.i10C. The crystal has a half-wave retardation voltage of 1,410 volts whichis less than half that of the widely used electro-optic material LiNbOIn an alternate method a mixture of the niobates of potassium, sodiumand barium can be used instead of the carbonates thereof. The niobatesof the above metals are prepared by heating a mixture of the metalcarbonates and Nb O at 900 to 1,150 C. The metal niobates thus obtainedare treated in the same fashion as the metal carbonates above.

In the same fashion disclosed in Example 7 above, several ternary singlecrystal solid solutions are prepared. Examples 8-2l are given in ensuingTable 2, and Examples 22-28 are given in Table 3. The Curie temperatureof the ternary crystal compositions together with the lattice constants(a and c given in angstroms, the melting points of the crystaltemperature at which twinning disappears, and the melt compositions usedto grow the crystals are given in ensuing Tables 2 and 3. The foregoingmaterials were prepared by mixing appropriate amounts of startingmaterials and treating them as in Example 2.

TABLE 2 Composition and properties of crystals pulled from melts of(KNbOs) x (NaNbOa) (B8Nb20u) I Crystal composition from chemicalanalysis, mole percent Melt composition mole percent Crystal propertiesTwin structure dlsap- Curie Lattice parameters pears at T., tempera-KNbOa NaNbO; BaNbzOa KNbO; N aNbOa BaNbzOa C. ture, C. as, A. co, A.

Crystal composition from chemical Molt composition mole percentanalysis, mole percent Crystal properties Twin structure disap- CurieLattice parameters pears at T., tempera- KNbO; NeNbO; BflNbzOa KNbOaNaNbO BaNbgO C. turc, C. as, A. Co, A.

10. 10. 80. 03.3 04. B 91.2 Structure O5. 70. 08.3 01.6 90.1 Structure nPsnudo'totmgonnl pnrnmoter, optical interference patterns indicatebiaxial symmetry.

No twins at 20 C. 0 BaNbzOu.

TABLE 3 Composition and properties of crystals pulled from melts of(RbNbOa):(NaNbOQABaNbzOo) I Crystal composition from chemical Twinstruc- Meas e WW ENBQQ- Crystal properties Melt composition, molepercent analysis mole percent ture disap- Curie Lattice parameters pearsat T., temp,

RbNbO NaNbO; BaNbaOa RbNbOs NaNbO; BaNbzOe 0. C. as, A. b0, A. Go, A

06. 7 26. 6 66. 7 1. 5 26. 5 72. 0 240 558 17. 609 17. 633 3. 998 16. 716. 6 66. 7 3. 7 18. 4 77. 8 140 505 17. 662 4. 007 16. 7 16.6 66.7 5.119.1 75. 8 1 .66 .007 10. 15. 75. 2. 4 20. 0 77. 6 158 496 17. 647 17.660 4. 005 20. 0 13. 3 66. 7 4. 0 18. 6 77. 4 85 460 17. 665 4. 006 26.7 0e. 6 66. 7 s. a 03. 2 88. a 15. 10. 75. 4. 2 01. 8 94. 0

8 Crystal from the frozen melt.

It has also been found that when the compositions described 30 will beunderstood by those skilled in the art that the foregoing TABLE 4Electrooptic constants T., V X10 Crystals pulled from melts of- C. voltcm./volt e3 1, 410 0. 86 Ko.aNau.2Ba2Nb5015 100 1, 190 0. 48 112 200 6400. 95 168 NaBazNbrOis 25 1, 570 0. 36 51 KSl'zNbrOrs 25 500 1. 3 400 Thephase diagram shown in FIG. 3 was determined for the (KNhO (SrNb Osystem by differential thermal analysis and X-ray methods. Thisestablished the existence of the solid solution region containing thetetragonal tungstenbronzc structure between X=0.l2 and 0.50. in the caseof other systems, X-ray analyses showed the presence of a tetragonaltungsten-bronze structure and the limits of solid solution. Also, withthe (NaNbO -(BaNbO O crystal growth from a solution of (NaNbO (BaNb Oresulted in a crystal composition near (NaNbO (BaNb O as determined bysodium analyses. This further demonstrates the existence of a solidsolution region, as indicated in FIG. 5.

In summary, transparent ferroelectric materials have been preparedhaving the general formulas x(ANbO lx)MNb 0 and A A, ,M Nb O, Thesematerials have a tetragonal tungsten-bronze type structure over a rangeof A to M concentrations. The materials are ferroelectric along theirC-axis with a large room temperature dielectric and linear electro-opticconstant.

While the invention has been particularly shown and described withreference to preferred embodiments thereof, it

and other changes in form and details may be made therein withoutdeparting from the spirit and scope of the invention.

What is claimed is:

LThe single crystalline ferroelectric composition xKNbO lx)SrNb O wherex is from about 0.45 to 0. l2.

2. The single crystalline ferroelectric composition xKNbO (lx)BaNb Owhere x is from about 0.35 to 0.25.

3. The single crystalline ferroelectric composition xRbNbO lx)SrNb Owhere x is from about 0.30 to 0.40.

4. The single crystalline ferroelectric composition xRbNbO lx)BaNb Owhere x is from about 0.30 to 0.35.

5. A single crystalline ternary ferroelectric composition grown from amelt composition in the triangular area defined y NaBa Nb O Rb Na Ba NbO and (NaNbO ),.,(BaNb 0 as shown in FIG. 8.

6. The single crystalline ternary ferroelectric composition having theformula s)|s.a( 3)fi.3( 2 6)15.4-

7. The single crystalline ternary ferroelectric composition having theformula a)ra.e( a)r:i.r( 2 o)13.3-

8. The single crystalline ternary ferroelectric composition having theformula a)3.s( a)22.o( 2 6)1a.9-

9. The single crystalline ternary ferroelectric composition having theformula s)r.5( a)2o.5( 2 s)12- 10. A method of preparing alkali-metalalkaline earth metal niobate binary compositions having the formulaxANbOy (lx)MNb O where A is at least one metal selected from the alkalimetals of the periodic table, M is at least one metal selected from thealkaline earth metals of the periodic table and where x is from 0.12 to0.50, comprising the steps of:

a. intimately mixing an alkali metal carbonate, an alkaline earth metalcarbonate, and niobium pentoxide; b. heating the mixture to atemperature from about l,l00

to about l,500 C;

c. forming a liquid phase of the resultant product; and

d. cooling said resultant product to thereby form a single crystal ofsaid alkali metal-alkaline earth metal niobate composition.

11. A method according to claim 10 wherein said alkali metal carbonateis sodium carbonate and said alkaline earth metal carbonate is bariumcarbonate.

12. A method according to claim 10 wherein said alkali metal carbonateis potassium carbonate and said alkaline earth metal carbonate isstrontium carbonate.

13. A method according to claim 10 wherein said alkali metal carbonateis potassium carbonate and said alkaline earth metal carbonate is bariumcarbonate.

14. A method according to claim 10 wherein said alkali metal carbonateis rubidium carbonate and said alkaline earth metal carbonate isstrontium carbonate.

15. A method according to claim 10 wherein said alkali metal carbonateis rubidium carbonate and said alkaline earth metal carbonate is bariumcarbonate.

16. A method according to claim 10 wherein said single crystal of analkali-metal, alkaline earth metal niobate composition is grown from amelt composition having the formula xNaNbO l.\:)BaNb O where x is about0.77 to about 0. l mole fractions.

17. A method according to claim wherein said single crystal of analkali-metal, alkaline earth metal niobate composition is grown from amelt composition having the formula xKNbO lx)BaNb O where x is about0.99 to about 0.38 mole fractions.

18. A method according to claim 10 wherein said single crystal of analkali-metal, alkaline earth metal niobate composition is grown from amelt composition having the formula xKNbO lx)SrNb O where x is about0.98 to about 0.12 mole fractions.

19. A method according to claim 10 wherein said single crystal of analkali-metal, alkaline earth metal niobate composition is grown from aternary melt composition in the area defined by a, b, c and d as shownin FIG. 6.

20. A method of preparing mixed alkali metals, alkaline earth metalniobate ternary compositions having the general formula (ANbO ),(ANbOMNb O where A is a first alkali metal ion, A is a second alkali metalion different from A, M is a metal selected from the alkaline earthmetals of the periodic table and x is about L5 to about l6.3, y is aboutL6 to about 26.5 and z is about 72.0 to about 94.0, comprising the stepsof:

a. intimately mixing a first alkali metal niobate, a second alkali metalniobate, and an alkaline earth metal niobate;

b. heating the mixture to a temperature of from about l,l00 to aboutl,500 C; c. forming a liquid phase of the resultant composition, and d.slowly cooling said resultant composition to thereby form a singlecrystal of said mixed alkali metal alkaline earth metal niobatecompositions.

21. A method according to claim 20 wherein said first alkali metalniobate is potassium niobate said second alkali metal niobate is sodiumniobate, said alkaline earth metal niobate is barium niobate and wherex=3.5, y=22.6 and z=73.9.

22. A method according to claim 20 wherein said first alkali metalniobate is potassium niobate, said second alkali metal niobate is sodiumniobate, said alkaline earth metal niobate is barium niobate and wherex=l6.3, y=8.3, and z==75.4.

23. A method according to claim 20 wherein said first alkali metalniobate is potassium niobate, said second alkali metal niobate is sodiumniobate, said alkaline earth metal niobate is barium niobate and wherex=13.6, y=l3. l, and z=73.3.

24. A method according to claim 20 wherein said first alkali metalniobate is potassium niobate, said second alkali metal niobate is sodiumniobate, said alkaline earth metal niobate is barium niobate and whereF56 y=l6.l and z=78.3.

25. A method according to claim 20 wherein said first alkali metalniobate is rubidium niobate, said second alkali metal niobate is sodiumniobate and said alkaline earth metal niobate is barium niobate andwhere x=l .5, y=26.5, and F720.

26. A method according to claim 20 wherein said first alkali metalniobate is rubidium niobate, said second alkali metal niobate is sodiumniobate and said alkaline earth metal niobate is barium niobate andwhere x=3.8, y=l 8.4, and z=77.8

27. A method according to claim 20 wherein said single crystal of mixedalkali metals, alkaline earth metal niobate composition is grown from aternary melt composition in the triangular area defined by NaBa Nb O RbNa Ba Nb O and (NaNbO BaNb O as shown in H6. 8.

2. The single crystalline ferroelectric composition xKNbO3.(1-x)BaNb2O6where x is from about 0.35 to 0.25.
 3. The single crystallineferroelectric composition xRbNbO3.(1-x)SrNb2O6 where x is from about0.30 to 0.40.
 4. The single crystalline ferroelectric compositionxRbNbO3.(1-x)BaNb2O6 where x is from about 0.30 to 0.35.
 5. A singlecrystalline ternary ferroelectric composition grown from a meltcomposition in the triangular area defined by NaBa2Nb5O15;Rb0.65Na0.35Ba2Nb5O15; and (NaNbO3)18(BaNb2O6)82 as shown in FIG.
 8. 6.The single crystalline ternary ferroelectric composition having theformula (KNbO3)16.3(NaNbO3)8.3(BaNb2O6)75.4.
 7. The single crystallineternary ferroelectric composition having the formula(KNbO3)13.6(NaNbO3)13.1(BaNb2O6)73.3.
 8. The single crystalline ternaryferroelectric composition having the formula(KNbO3)3.5(NaNbO3)22.6(BaNb2O6)73.9.
 9. The single crystalline ternaryferroelectric composition having the formula(RbNbO3)1.5(NaNbO3)26.5(BaNb2O6)72.
 10. A method of preparingalkali-metal alkaline earth metal niobate binary compositions having theformula xANbO3.(1-x)MNb2O6 where A is at least one metal selected fromthe alkali metals of the periodic table, M is at least one metalselected from the alkaline earth metals of the periodic table and wherex is from 0.12 to 0.50, comprising the steps of: a. intimately mixing analkali metal carbonate, an alkaline earth metal carbonate, and niobiumpentoxide; b. heating the mixture to a temperature from about 1,100* toabout 1,500* C; c. forming a liquid phase of the resultant product; andd. cooling said resultant product to thereby form a single crystal ofsaid alkali metal-alkaline earth metal niobate composition.
 11. A methodaccording to claim 10 wherein said alkali metal carbonate is sodiumcarbonate and said alkaline earth metal carbonate is barium carbonate.12. A method according to claim 10 wherein said alkali metal carbonateis potassium carbonate and said alkaline earth metal carbonate isstrontium carbonate.
 13. A method according to claim 10 wherein saidalkali metal carbonate is potassium carbonate and said alkaline earthmetal carbonate is barium carbonaTe.
 14. A method according to claim 10wherein said alkali metal carbonate is rubidium carbonate and saidalkaline earth metal carbonate is strontium carbonate.
 15. A methodaccording to claim 10 wherein said alkali metal carbonate is rubidiumcarbonate and said alkaline earth metal carbonate is barium carbonate.16. A method according to claim 10 wherein said single crystal of analkali-metal, alkaline earth metal niobate composition is grown from amelt composition having the formula xNaNbO3.(1-x)BaNb2O6 where x isabout 0.77 to about 0.15 mole fractions.
 17. A method according to claim10 wherein said single crystal of an alkali-metal, alkaline earth metalniobate composition is grown from a melt composition having the formulaxKNbO3.(1-x)BaNb2O6 where x is about 0.99 to about 0.38 mole fractions.18. A method according to claim 10 wherein said single crystal of analkali-metal, alkaline earth metal niobate composition is grown from amelt composition having the formula xKNbO3.(1-x)SrNb2O6 where x is about0.98 to about 0.12 mole fractions.
 19. A method according to claim 10wherein said single crystal of an alkali-metal, alkaline earth metalniobate composition is grown from a ternary melt composition in the areadefined by a, b, c and d as shown in FIG.
 6. 20. A method of preparingmixed alkali metals, alkaline earth metal niobate ternary compositionshaving the general formula (ANbO3)x(A''NbO3)y(MNb2O6)z where A is afirst alkali metal ion, A'' is a second alkali metal ion different fromA, M is a metal selected from the alkaline earth metals of the periodictable and x is about 1.5 to about 16.3, y is about 1.6 to about 26.5 andz is about 72.0 to about 94.0, comprising the steps of: a. intimatelymixing a first alkali metal niobate, a second alkali metal niobate, andan alkaline earth metal niobate; b. heating the mixture to a temperatureof from about 1,100* to about 1,500* C; c. forming a liquid phase of theresultant composition, and d. slowly cooling said resultant compositionto thereby form a single crystal of said mixed alkali metal alkalineearth metal niobate compositions.
 21. A method according to claim 20wherein said first alkali metal niobate is potassium niobate said secondalkali metal niobate is sodium niobate, said alkaline earth metalniobate is barium niobate and where x 3.5, y 22.6 and z 73.9.
 22. Amethod according to claim 20 wherein said first alkali metal niobate ispotassium niobate, said second alkali metal niobate is sodium niobate,said alkaline earth metal niobate is barium niobate and where x 16.3, y8.3, and z 75.4.
 23. A method according to claim 20 wherein said firstalkali metal niobate is potassium niobate, said second alkali metalniobate is sodium niobate, said alkaline earth metal niobate is bariumniobate and where x 13.6, y 13.1, and z 73.3.
 24. A method according toclaim 20 wherein said first alkali metal niobate is potassium niobate,said second alkali metal niobate is sodium niobate, said alkaline earthmetal niobate is barium niobate and where x 5.6, y 16., and z 78.3. 25.A method according to claim 20 wherein said first alkali metal niobateis rubidium niobate, said second alkali metal niobate is sodium niobateand said alkaline earth metal niobate is barium niobate and where x 1.5,y 26.5, and z 72.0.
 26. A method according to claim 20 wherein saidfirst alkali metal niobate is rubidium niobate, said second alkali metalniobate is sodium niobate and said alkaline earth metal niobate isbarium niobate and where x 3.8, y 18.4, and z 77.8
 27. A methodaccording to claim 20 wherein said single crystal of mixed alkalimetals, alkaline earth metal niobate composition is grown from a ternarymelt composition in the triangular area defined by NaBa2Nb5O15;Rb0.65Na0.35Ba2Nb5O15; and (NaNbO3)18(BaNb2O6)82 as shown in FIG. 8.